1. Field of the Invention
The present invention relates to a method and apparatus for the introduction of a percutaneous flexible lead member and, particularly, to a method and apparatus for the introduction of a flexible neurostimulator lead into the epidural space of the spinal cord of a patient.
2. Description of the Prior Art
Chronically implantable stimulators for the brain and spinal cord have been in use for some time. Originally these were used to treat chronic intractable pain. Clinically favorable results were reported in a number of publications including "Long Term Follow Up of Dorsal Cord Stimulation for Chronic Pain Syndrome After Multiple Lumbar Operations", Applied Neurophysiology, Volume 45, pages 201-204, 1982 by J. Siegfried and Y. Lazorthes and "Spinal Epidural Neurostimulation for Treatment of Acute and Chronic Intractable Pain: Initial and Long Term Results", Neurosurgery, Volume 5, pages 344-348, 1979, by R. R. Richardson, et al.
Subsequently, additional medical applications were reported including treatment of peripheral vascular disease as seen in "Spinal Cord Stimulation in Peripheral Vascular Disease" Proceedings on Functional Electrostimulation, 1983, by E. H. Sedgwick, L. S. Illis, and R. C. Tallis. Research continues in the possible treatment of angina and other disorders by spinal cord stimulation. Spinal cord stimulation also has been used in treating multiple sclerosis, spinal cord injury, cerebral palsy, amyotrophic lateral sclerosis, dystonia, torticollis and other neurological disorders. The use of electrical stimulation of peripheral nerves and spinal cord to promote recovery from trauma and to accelerate nerve regeneration also has been proposed. In addition, spinal cord stimulation has been proposed to induce locomotion.
The earliest practical spinal cord stimulators were passive devices which picked up RF energy transmitted across the skin and applied it via electrodes implanted near the spinal cord. Many medical applications are yet best approached with such a device. The PISCESa family of spinal cord stimulation systems made available to the medical community by Medtronic, Inc. of Minneapolis, Minn., assignee of the present invention, are examples of passive spinal cord stimulation systems.
A later development in neurological stimulation is the chronically implantable active stimulation system. These consist of a battery operated pulse generator which is electrically coupled to the spinal cord by insulated leads coupled to electrodes normally implanted in the epidural space. The Itrel IIa implantable pulse generator manufactured by Medtronic, Inc., is an example of an active device that has advanced programmable features permitting mode changes by transcutaneous RF telemetry. These mode changes include modifying the stimulation intensity. A number of different lead designs have been employed for placement of one or more electrodes in the epidural space including the PISCES-SIGMAa GENERATION II or PISCESa GENERATION II epidural leads available from Medtronic, Inc.
These neural stimulation electrodes and leads implanted in the epidural space of the spinal cord of a patient for stimulating selected locations along the spinal cord, usually for the relief of pain. The leading distal end of the lead is axially moved along the epidural space in the spinal cord by passing the end through a Tuohy needle and pushing the end of the lead to the location on the dura where it is to stimulate the spinal cord. These leads have a special configuration at their distal ends and adjacent the stimulating electrodes which may be straightened during installation of the lead by a stylet which passes through the lead to ease its introduction. Once the lead has been positioned as desired, the lead stylet is removed to cause the distal end of the lead to resume its normal configuration to minimize subsequent axial or lateral movement of the lead once it has been placed. In these leads, the leading distal end of the lead is inaccessibly located in the epidural space at all times during introduction and fixation and, therefore, is capable of being manipulated, only from the other end thereof.
The aforementioned installation and fixation procedure is illustrated in FIGS. 1 and 2, which depict the operative procedure of introducing one of the aforementioned leads into the epidural space 10 adjacent the spinal cord 12. A Tuohy needle 14, which is usually between 14 and 18 gauge, and a stylet for stiffening the thin-walled needle are inserted into the interspinous ligament between adjacent vertebrae 20 and 22 until the tip of the needle is advanced through the ligamentum flavum and into the epidural space 10. The stylet is then withdrawn and a wire guide is inserted through the needle into the epidural space under fluoroscopic control to identify the pathway that the lead will take.
Penetration of the ligamentum flavum may be confirmed by withdrawing the stylet and filling the needle lumen with saline solution, which rapidly drains when penetration is achieved. The operative procedure is repeated until an appropriate pathway is identified.
Thereafter, the wire guide is removed and one of the aforementioned leads is inserted through the needle through the epidural space. Under fluoroscopic control, the lead is advanced to an appropriate spinal level under manipulation of the needle and lead itself. The lead depicted in FIG. 2 in the epidural space possesses a relaxed curved shape which is straightened during insertion by the lead stylet 22 shown extending from the straight-line connector 24 of the proximal end of the lead body. Once the lead has been positioned as desired, and electrical stimulation tests have been completed, the proximal end of the lead is coupled to the PISCESa spinal cord stimulation system RF receiver or the Itrel IIa implantable pulse generator.
The Tuohy needle and stylet conventionally used in such implants possesses a sharpened, curved Huber tip with a side opening to facilitate both the penetration of the subcutaneous fascia as well as the underlying interspinous ligament and ligamentum flavum and the direction of the wire guide and implantable lead at an angle to the axis of the introducer sheath as shown in FIGS. 1 and 2. The stylet is provided with a matching beveled end such that when it is fully inserted into the lumen of the introducer, the beveled surface may be lined up to the side opening to both stiffen the entire assembly and block the opening in the distal end of the needle, thereby easing its introduction. To avoid the inadvertent rotation of the stylet within the lumen of the needle during percutaneous advancement of the assembly, it has been conventional to provide a notch in the introducer hub which receives a complimentary lug on the stylet hub, as shown in FIGS. 2 and 3 of U.S. Pat. No. 4,512,351. During introduction, as shown for example in FIG. 7 of the '351 patent, manual force is applied to the two hubs to maintain the lug within the notch and prevent the inadvertent rotation or backing out of the stylet.
During such introduction, there is a tendency for the stylet to telescopically retract within the sheath when the medical attendant, nurse, doctor or the like is attempting to forcibly advance the tapered leading tip of the assembled introducer needle and stylet through the aforementioned tissue. This makes manipulation of the needle and stylet not only traumatic to the patient, but also awkward and imprecise for the medical attendant, who has to make certain that the stylet is not retracting or rotating in the process.